Boehringer Ingelheim , Biberach, Germany
5th HTRF Symposium, Avignon, France
Nowadays a plethora of assays is available to identify ligands for G-protein coupled receptors (1, 2) including binding assays using either radiolabelled or fluorescent labelled ligands. Although binding assays have the limitation that they cannot discriminate between agonist and antagonist activity of ligands, they can provide valuable information in terms of ligand binding kinetics/target residence time to support structure activity relationships. Furthermore they can help to dissect the effects of modulators on the affinity and efficacy of a GPCR ligand probe. Recently binding assays have been used to screen fragments at high concentrations. (3, 4). Tag-lite® binding assays provide an alternative to costly and time consuming radioligand binding assays. Data from optimization experiments of Tag-lite®-lite binding assays for a class B receptor will be presented. Furthermore it will be shown how the technology can be used to detect different effects of a potential negative allosteric modulator on the efficacy and affinity of a fluorescently labelled ligand probe.